There are SO many international symbols and acronyms used in photography. In the last couple of articles I’ve tried to explain what some of those letters and symbols are on your camera dial. This month I’d like to explain what some other letters mean.

ISO is a standard of film speed or sensor sensitivity.

The ISO numbers give us understanding of how much light will be needed to make our exposure.

Us older photographers may remember setting the ASA or DIN on our film speed dial back when all there was were film cameras. ISO is an acronym for International Standards Organization, ASA is the Standards American Association, and DIN, mostly used in Europe, was Deutsch Index Number. We bought our film according to the kind of photography we would be doing. A slow speed film with a ASA/ISO of say 50 or 100 was good for photographs when there was plenty of light, during the middle of the day.

If we needed to photograph indoors or in low light situations we would look for a faster film with a higher ASA/ISO of say 400 or 800. Slow speed, fine grain film (low ISO number) has smaller silver crystals that needed more light to excite them to make an image. But the image quality was better because the grains were smaller and more tightly packed together. As more people wanted to shoot in lower light, the film manufacturers found that by putting larger silver crystals on the film gave the film more speed (less light was needed to expose the film).

As the film speeds increased to 800, 1600, and higher, they found that the bigger grains of the crystals became visible in the final print. Some people liked the ability to shoot in lower light and the film grain didn’t bother them. Others, that were more interested in fine prints, found that the finer grained film produced finer results and was worth the film needing to be exposed a little longer.

Although I have been talking about film here, the same applies to a digital camera’s sensor.

In digital cameras there is a sensor in place where the film used to be in film cameras.

The lower the ISO, the more light you will need to make a proper exposure, the higher the ISO the less light you will need. The advantage of digital cameras is that you can use a different ISO for every picture if you need to. With film you had to finish the whole roll of film before changing to a different ISO film.

So with a low ISO setting you will need more light to make a properly exposed image than with a high ISO setting, but the quality of the printed photograph will be better.

As you begin to use higher ISO settings the more the sensor will record electronic noise which will start showing up in the photograph. It will not be visible to your eyes as you look through the viewfinder, but it will show up on your image.

Film will not do this, so it is a better choice for long exposures like my star trails photograph where I opened up the shutter and left it open while I went back to sleep in my tent, then woke up a few hours later to close it. It results in a stunning photograph of the stars streaking through the black night sky. Interestingly it also records the colors of each different star. Most people think stars are all white until you see my photograph where they are blue, yellow, red, orange and purple.

So how does one know which ISO to use?

First turn off the automatic ISO feature on your camera so you know what ISO you’re using.

If you are in a low light situation turn on the noise reduction feature. *Note-using this feature might result in an image that is not as sharp as you would like.

Always set your ISO to the lowest setting (which is 200 if it’s a Nikon.) Canon has a lowest ISO setting of 100.

If you need more light for an inside shot turn up the ISO to the lowest number that will give you the exposure that you want. (See my histogram art article for more information on correct exposures.)

Most of the time I am disappointed with the image quality of an ISO of over 540.

You can get a sense of what noise looks like by looking at your TV when it is between channels. It looks like static. It usually appears in low light situations, especially if you’re inside and not using a flash. If you do happen to take a photograph that has noise in it you can fix some of it in Photoshop or with a software program like Noise Ninja, but the image loses a lot of detail by doing this. So… the moral here is to try to always get the best image you can through the settings on your camera, not just hope to fix it in Photoshop.

Gene Rodman is a life long photographer and owns Montana Photographic Arts Gallery and Studio. You can view his website at http://www.MTPhotoArts.com.